In many instances, such a power-distribution network must conform to an existing layout of switches or other loads to be energized thereby and thus must allow for widely varying distances between these loads and the power source. In the event of a breakdown, such as a short circuit or a ground fault, the affected part of the network must be quickly isolated from the remainder and must be limited in its extent so as to insure continued operation of as many loads as possible. Moreover, the isolated network part should be readily accessible for repair and restoration to service.
When loads require alternating current for their operation but the power supply is a DC source, as is generally the case in telephone exchanges and the like, DC/AC converters must be inserted between these loads and corresponding lines of the distribution network. To prevent any objectionable retroaction of the chopping frequencies of the converters upon the distribution network, suitable low-pass or band-stop filters should be provided upstream of the converters to suppress these frequencies.
The installation of overload-responsive circuit breakers at strategic points of a power-distribution network helps localize the effects of a fault. This, however, does not prevent a temporary drop in the supply voltage due to a current surge caused by a short circuit in the network. Especially with loads remote from the source, whose supply lines are relatively long so as significantly to delay the restoration of the input voltage to its normal level, the resulting interruption of operating current may be highly detrimental.